Information recording method and optical recording medium therefor

ABSTRACT

An information recording method including irradiating a phase change recording layer of an optical recording medium with either a multi-pulse laser light train having a recording power of Pw or laser light having an erasing power Pe to record a mark having a length nT in the recording layer, wherein n is an integer of from 3 to 14 and T represents a clock cycle, wherein the multi-pulse laser light train has a constitution such that a heating pulse and a cooling pulse are alternated and the number of heating pulses and the number of cooling pulses each increases by 1 when n increases by 2, and wherein when n is from 6 to 14, the last heating pulse and last cooling pulse have a pulse width of from 0.5T to 0.9T and from 0.7T to 1.5T, respectively.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an information recording methodfor recording information in a recording medium having a recording layerwhich can reversibly achieve a crystal phase and an amorphous state byirradiating the recording layer with a multi-pulse laser light trainemitted from a light source, and an optical recording medium for theinformation recording method.

[0003] 2. Discussion of the Background

[0004] Along with the popularization of multimedia, playback-onlyoptical recording media (hereinafter sometimes referred to as media)such as audio CDs and CD-ROMs and information reproduction apparatushave been developed and practically used. Recently, not only recordableoptical discs using a dye medium and rewritable magnetooptic discs (MOs)using a magnetooptic medium, but also phase change type media attractattention.

[0005] Such phase change type media includes a material having a phasechange property of reversibly achieving a crystal phase and an amorphousstate and information is recorded therein utilizing the property.Information can be recorded in the phase change type media and therecorded information can be reproduced, using only laser light emittedfrom a laser diode (i.e., without using an external magnetic field),which is needed for recording information in MOs. In addition, it ispossible to perform overwriting in which information can be recordedwhile erasing previously recorded information using laser light at thesame time.

[0006] A typical waveform of recording laser light pulses for use inrecording information in a phase change recording medium is the waveformof single pulse laser light emitted by a laser diode which isillustrated in FIG. 17 and which is generated according to, for example,an Eight Fourteen Modulation code (i.e., EFM). As can be understood fromthe waveform illustrated FIG. 17, the recording power PWA is set so asto be higher than the read power PR. When a pulse having such a waveformis applied to a phase change recording medium, problems such that theresultant recording mark deforms like a tear drop, and marks having alow reflectance against laser light cannot be obtained because theirradiated portion of the recording layer achieves an incompleteamorphous state due to slow cooling speed of the recorded mark.

[0007] In attempting to solve such problems, an information recordingmethod which is illustrated in FIG. 18 is proposed for recordinginformation in a phase change recording medium. In the method, asillustrated in FIG. 18, a mark is formed on a phase change recordingmedium by irradiating the-recording medium with laser light which has amulti-pulse emission waveform and multilevel recording powers and whichis generated according to an EFM code.

[0008] When a mark is recorded in a phase change recording medium usingthe multi-pulse laser light train, the corresponding portion of themulti-pulse laser light is constituted of a first heating pulse A bywhich the recording layer of the recording medium is preliminarilyheated so as to be heated to a temperature not lower than the meltingpoint thereof, plural heating pulses B which follow the first heatingpulse A and by which the recording layer is further heated, pluralcooling pulses which are located between the first heating pulse A andthe top of the heating pulses B and between the heating pulses B, and alast cooling pulse C. In the method, the following relationship issatisfied:

PWB PWA PWC≈PR

[0009] wherein PWB represents the emission power of the heating pulse B,PWA represents the emission power of the first heating pulse A, PWCrepresents the emission power of the cooling pulse C and PR representsthe read power.

[0010] When erasing a mark previously formed in a phase change recordingmedium using the multi-pulse laser light train, the correspondingportion of the multi-pulse laser light train is constituted of an erasepulse D. The emission power PED of the erase pulse D is set so as tosatisfy the following relationship:

PWC<PED<PWA.

[0011] When this recording method is used, the mark area of therecording layer achieves an amorphous state because the heated area israpidly cooled, and the space area achieves a crystal state because thearea is heated and then gradually cooled without forcible cooling. Thus,the recording medium has a large reflectance difference between the mark(i.e., the area in an amorphous state) and space (i.e., the area in acrystal state).

[0012] The methods for recording information in an optical recordingmedia are classified into a mark position recording method (i.e., PulsePosition Modulation, PPM) and a mark edge recording method (i.e., PulseWidth Modulation, PWM). Recently, the mark edge recording method istypically used because of being able to be used for high densityrecording. When information is recorded in a phase change recordingmedium by a mark edge recording method, the heating pulse typically hasa pulse width of 0.5T and the cooling pulse also has a pulse width of0.5T, wherein T represents a record channel clock cycle.

[0013] Namely, information is recorded in a phase change recordingmedium using laser light having a multi-pulse emission waveform in whicha pair of a heating pulse and a cooling pulse is added whenever the marklength (i.e., mark data length) of recording data increases by 1T. FIG.19 illustrates a typical example of the recording waveform. When highspeed recording is performed using this method, the record channel clock(T) is highly frequented at the same rate as that of the linearrecording speed, for example, at a rate of twice or four times, withoutchanging the record waveform.

[0014] However, as the recording speed increases, the width of theheating pulse and cooling pulse seriously decreases, and thereby itbecomes impossible to heat the recording layer so as to reach theheating temperature (i.e., the amorphous temperature) and the coolingtemperature (i.e., the crystal temperature), at which the recordinglayer can change the phase, resulting in formation of incomplete marks.Thus, a problem in that the mark does not have a predetermined marklength occurs.

[0015] In attempting to solve the problem, Unexamined Japanese PatentApplication No. (hereinafter referred to as JP-A) 9-134525 discloses aninformation recording method in which a recording mark having a desiredmark length is recorded in a recording layer at a high speed by heatingand cooling the recording layer for a time enough to sufficiently heatand cool the recording layer without driving a light source driver at ahigh speed. Specifically the recording method is such that a lightsource irradiates a phase change recording layer with a first heatingpulse followed by plural rear heating pulses, plural rear cooling pulseswhich are emitted between the first heating pulse and the top of therear heating pulses and between the plural rear heating pulses, and alast cooling pulse to record a mark therein, wherein when data having amark length of nT (n is odd or even numbers, and T represents a recordchannel clock cycle) are recorded, the pulse width of the rear heatingpulses and rear cooling pulses is substantially the same as the recordchannel clock cycle.

[0016] In addition, an optical recording medium which has a GeSbTerecording layer and in which information can be recorded in therecording layer at a speed 4.8 times the recording speed of DVD usingthe information recording method disclosed in JP-A 9-134525 is disclosedin Optical Data Storage (ODS) 2000 Technical Digest (pp. 135-143).

[0017] However, when information is repeatedly recorded in a melt-erasemode in the optical recording medium disclosed in ODS 2000 TechnicalDigest at a speed 4.8 times the DVD speed (i.e., at a speed of 16.8 m/s)using the information recording method disclosed in JP-A 9-134525, thespace area of the recording medium does not perfectly achieve acrystallization state (i.e., a part of the space area maintains theamorphous state) because the crystallization speed of the recordingmedium is not fast enough to match the recording speed, i.e., therecording medium has poor repeat recording properties.

[0018] In attempting to solve the problem (i.e., to avoid amorphism ofan space area),ODS 2000 Technical Digest discloses a method in whichrecording is repeatedly performed while the erasing power Pe isdecreased to a power such that the recording layer is not fused.However, the recording properties of the information recorded by themethod are inferior to those of the information recorded in a melt-erasemode.

SUMMARY OF THE INVENTION

[0019] Accordingly, an object of the present invention is to provide anoptical recording medium in which information can be repeatedly recordedin a melt-erase mode at a speed four to five times that of the DVD-ROMplayback speed (i.e., at a speed of from 14 to 17.5 m/s) and at arecording density equal to or higher than the DVD-ROM recording density.

[0020] Another object of the present invention is to provide aninformation recording method by which information can be recorded in theoptical recording medium at a high speed while the recorded informationhas good recording properties.

[0021] To achieve such objects, the present invention contemplates theprovision of an information recording method including:

[0022] Irradiating a phase-change recording layer of an opticalrecording medium with either a multi-pulse laser light train having arecording power of Pw or laser light having an erasing power Pe to allowthe phase change recording layer to reversibly achieve a crystal stateand an amorphous state, thereby recording a mark having a length nT inthe recording layer, wherein n is an integer of from 3 to 14 and Trepresents a clock cycle,

[0023] wherein the multi-pulse train has a constitution such that aheating pulse and a cooling pulse are alternated, wherein the number ofheating pulses and the number of cooling pulses each increases by onewhen n increases by two, and wherein when n is from 6 to 14, a lastheating pulse has a pulse width of from 0.5T to 0.9T and a last coolingpulse has a pulse width of from 0.7T to 1.5T.

[0024] It is preferable that a first heating pulse has a pulse width offrom 0.7T to 1.3T and a rear heating pulse, which is located between thefirst heating pulse and the last heating pulse, has a pulse width offrom 0.8T to 1.4T.

[0025] When n is 3, it is preferable that the first heating pulse has awidth of from 0.8T to 1.4T and the last cooling pulse has a width offrom 1.1T to 1.9T.

[0026] When n is 4, it is preferable that the first heating pulse has awidth of from 0.6T to 1.4T, the last heating pulse has a width of from0.1T to 0.8T and the last cooling pulse has a width of from 0.8T to1.7T.

[0027] When n is 5, it is preferable that the first heating pulse has awidth of from 0.5T to 1.6T, the last heating pulse has a width of from0.6T to 1.2T and the last cooling pulse has a width of from 0.7T to1.6T.

[0028] The ratio (Pe/Pw) of the erasing power (Pe) to the recordingpower (Pw) is preferably from 0.4 to 0.7.

[0029] In addition, it is preferable that the recording layer has aformula of GeαGaβSbγTe100-α-β-γ, wherein α is a number of from 1 to 5 inunits of atomic percent, β is a number of from 1 to 5 in units of atomicpercent, and γ is a number of from 70 to 81 in units of atomic percent.

[0030] Further, it is preferable that the upper limit of therecrystallization linear speed, below which the recording layer heatedby the laser light having a power of Pe recrystallizes is from 14 m/s to20 m/s.

[0031] Furthermore, it is preferable that the recording layer has such aproperty as to crystallize at a temperature of from 160 to 210° C. whenheated at a heating speed of 10° C./min.

[0032] As another aspect of the present invention, an optical recordingmedium is provided which includes

[0033] a substrate;

[0034] a recording layer located overlying the substrate, wherein therecording layer has a formula of GeαGaβSbγTe100-α-β-γ, wherein α is anumber of from 1 to 5 in units of atomic percent, β is a number of from1 to 5 in units of atomic percent, and γ is a number of from 70 to 81 inunits of atomic percent; and

[0035] a reflection layer located overlying the recording layer.

[0036] These and other objects, features and advantages of the presentinvention will become apparent upon consideration of the followingdescription of the preferred embodiments of the present invention takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIG. 1 is a block diagram illustrating the first embodiment of theinformation record/reproduction apparatus utilizing the informationrecording method of the present invention;

[0038]FIG. 2 is a timing chart illustrating the channel clock and thewaveforms of the multi-pulse laser light train in the first embodimentof the information record/reproduction apparatus;

[0039]FIG. 3 is a diagram illustrating the mark lengths of record marksto be recorded and the first heating pulse A, rear cooling pulses C1-C6,rear heating pulses B1-B5, last heating pulse Br, and last cooling pulseCr of the multi-pulse laser light train;

[0040]FIG. 4 is a graph illustrating the relationship between the pulsewidth (0.4 to 1.0T) of the last heating pulse Br and the jittercharacteristic (σ/Tw) when a record mark having a mark length of from 6Tto 14T is recorded in Example 1;

[0041]FIG. 5 is a graph illustrating the relationship between the pulsewidth (0.6 to 1.4T) of the last cooling pulse Cr and the jittercharacteristic (σ/Tw) when a record mark having a mark length of from 6Tto 14T is recorded in Example 1;

[0042]FIG. 6 is a graph illustrating the relationship between the pulsewidth (0.7 to 1.5T) of the rear heating pulses B1-B5 and the jittercharacteristic (σ/Tw) when a record mark having a mark length of from 6Tto 14T is recorded in Example 1;

[0043]FIG. 7 is a graph illustrating the relationship between the pulsewidth (0.6 to 1.4T) of the first heating pulse A and the jittercharacteristic (σ/Tw) when a record mark having a mark length of from 6Tto 14T is recorded in Example 1;

[0044]FIG. 8 is a graph illustrating the relationship between the pulsewidth (0.7 to 1.5T) of the first heating pulse A and the jittercharacteristic (σ/Tw) when a record mark having a mark length of 3T isrecorded in Example 1;

[0045]FIG. 9 is a graph illustrating the relationship between the pulsewidth (1.0 to 2.0T) of the last cooling pulse Cr and the jittercharacteristic (σ/Tw) when a record mark having a mark length of 3T isrecorded in Example 1;

[0046]FIG. 10 is a graph illustrating the relationship between the pulsewidth (0.5 to 1.5T) of the first heating pulse A and the jittercharacteristic (σ/Tw) when a record mark having a mark length of 4T isrecorded in Example 1;

[0047]FIG. 11 is a graph illustrating the relationship between the pulsewidth (0.1 to 0.9T) of the last heating pulse Br and the jittercharacteristic (σ/Tw) when a record mark having a mark length of 4T isrecorded in Example 1;

[0048]FIG. 12 is a graph illustrating the relationship between the pulsewidth (0.7 to 1.8T) of the last cooling pulse Cr and the jittercharacteristic (σ/Tw) when a record mark having a mark length of 4T isrecorded in Example 1;

[0049]FIG. 13 is a graph illustrating the relationship between the pulsewidth (0.4 to 1.7T) of the first heating pulse A and the jittercharacteristic (σ/Tw) when a record mark having a mark length of ST isrecorded in Example 1;

[0050]FIG. 14 is a graph illustrating the relationship between the pulsewidth (0.5 to 1.3T) of the last heating pulse Br and the jittercharacteristic (σ/Tw) when a record mark having a mark length of ST isrecorded in Example 1;

[0051]FIG. 15 is a graph illustrating the relationship between the pulsewidth (0.6 to 1.7T) of the last cooling pulse Cr and the jittercharacteristic (σ/Tw) when a record mark having a mark length of ST isrecorded in Example 1;

[0052]FIG. 16 is a graph illustrating the relationship between the ratioPe/Pw of the erasing power (Pe) to the recording power (Pw) and thejitter characteristic when recording is repeatedly performed;

[0053]FIG. 17 is a diagram illustrating a typical waveform of a pulsefor use in conventional single-pulse optical recording when a markhaving a mark length of 5T is recorded in a phase change recordingmedium;

[0054]FIG. 18 is a diagram illustrating a typical waveform of amulti-pulse laser light train for use in conventional multi-pulserecording when a mark having a mark length of 5T is formed on a phasechange recording medium, wherein the laser light has a multilevelrecording power and is generated according to an EFM code; and

[0055]FIG. 19 is a diagram illustrating typically examples of thewaveforms of a multi-pulse laser light train in which a pair of aheating pulse and a cooling pulse are added whenever the mark length ofrecord data increases by 1T.

DETAILED DESCRIPTION OF THE INVENTION

[0056]FIG. 1 is a block diagram illustrating the first embodiment of theinformation record/reproduction apparatus utilizing the informationrecording method of the present invention. FIG. 2 is a timing chartillustrating the channel clock and the waveforms of the multi-pulselaser light train in the first embodiment of the informationrecord/reproduction apparatus. This information record/reproductionapparatus records (i.e., overwrites) information in a phase changerecording medium and reproduces the recorded information. The apparatusperforms mark edge recording (i.e., PWM) using an EFM code.

[0057] The information record/reproduction apparatus includes a digitalcircuit (not shown) serving as a light intensity control device; a laserdiode driving circuit; a laser diode LD serving as a light source of anoptical head; a spindle motor configured to rotate a phase changerecording medium; the optical head: and an optical system.

[0058] When recording is performed, the digital circuit generates pulsecontrol signals according to EFM data. The laser diode driving circuitgenerates driving current according to the pulse control signals todrive the laser diode LD. Thus, multi-pulse laser light having waveformsas illustrated in FIG. 2 is emitted. The optical head irradiates a phasechange recording medium, which is rotated by the spindle motor, with themulti-pulse laser light train emitted by the laser diode LD via theoptical system. Thus, record marks are formed in the recording layer ofthe phase change recording medium, resulting in record of information inthe optical recording medium.

[0059] The multi-pulse laser light emitted by the laser diode LD areconstituted of a first heating pulse A, followed by one or more rearheating pulses B (B1, B2, . . . and B5, in the order from the top to thelast); a last heating pulse Br which follows the rear heating pulses B;one or more rear cooling pulses C (C1, C2, . . . and C6, in the orderfrom the top to the last) which are located between the first heatingpulse A and the top of the rear heating pulses B, between the pluralrear heating pulses B, and between the last of the plural rear heatingpulses B and the last heating pulse Br; and a last cooling pulse Cr.

[0060] When recording is performed (i.e., record marks having differentmark lengths are recorded), the multi-pulse laser light emitted by thelaser diode LD is as follows.

[0061] As illustrated in FIG. 2, a record mark having a mark length of3T (T is the cycle of the record channel clock) which is the shortestmark length is recorded by irradiating multi-pulse laser lightconstituted of a first heating pulse A and a last cooling pulse Cr. Arecord mark having a mark length of 4T or 5T is recorded by irradiatingmulti-pulse laser light constituted of a first heating pulse A, a rearcooling pulse C1, a last heating pulse Br and a last cooling pulse Cr,which are sequentially arranged in this order.

[0062] A record mark having a mark length of 6T or 7T is recorded byirradiating multi-pulse laser light constituted of a first heating pulseA, a rear cooling pulse C1, a rear heating pulse B1, a rear coolingpulse C2, a last heating pulse Br and a last cooling pulse Cr, which aresequentially arranged in this order.

[0063] A record mark having a mark length of 8T or 9T is recorded byirradiating multi-pulse laser light constituted of a first heating pulseA, a rear cooling pulse C1, a rear heating pulse B1, a rear coolingpulse C2, a rear heating pulse B2, a rear cooling pulse C3, a lastheating pulse Br and a last cooling pulse Cr, which are sequentiallyarranged in this order.

[0064] A record mark having a mark length of 10T or 11T is recorded byirradiating multi-pulse laser light constituted of a first heating pulseA, a rear cooling pulse C1, a rear heating pulse B1, a rear coolingpulse C2, a rear heating pulse B2, a rear cooling pulse C3, a rearheating pulse B3, a rear cooling pulse C4, a last heating pulse Br and alast cooling pulse Cr, which are sequentially arranged in this order;

[0065] A record mark having a mark length of 14T is recorded byirradiating multi-pulse laser light constituted of a first heating pulseA, a rear cooling pulse C1, a rear heating pulse B1, a rear coolingpulse C2, a rear heating pulse B2, a rear cooling pulse C3, a rearheating pulse B3, a rear cooling pulse C4, a rear heating pulse B4, arear cooling pulse C5, a rear heating pulse B5, a rear cooling pulse C6,a last heating pulse Br and a last cooling pulse Cr, which aresequentially arranged in this order.

[0066] Thus, one heating pulse and one cooling pulse are increased whenthe mark length increases by 2T. In addition, when record marks having amark length of from 6T to 14T are recorded, the last heating pulse Brpreferably has a pulse width of from 0.5T to 0.9T, and the last coolingpulse Cr preferably has a pulse width of from 0.7T to 1.3T.

[0067] As illustrated in FIG. 1, constant currents corresponding to theemission power for the first heating pulse A and rear heating pulses Bare applied to the laser diode LD from a current generator PW1 in thelaser diode driving circuit. Similarly, current generators PW2 and PW3apply constant currents corresponding to the emission powers of thecooling pulses C and an erase pulse D to the laser diode LD,respectively.

[0068] The light intensity control device (not shown) generates A and Bpulse control signals, C pulse control signals, and D pulse controlsignals according to EFM data. Switching elements 11, 12 and 13 put onor off the current generators PW1, PW2 and PW3 according to the A and Bpulse control signals, C pulse control signals, and D pulse controlsignals generated by the light intensity control device so that thelaser diode LD emits the multi-pulse laser light as illustrated in FIG.2.

[0069] When the recorded information is reproduced, the laser diodedriving circuit allows the laser diode LD to emit laser light byapplying a reproduction power (i.e., a read power) thereto. The opticalhead irradiates the phase change recording medium with the laser lightemitted by the laser diode LD and passing through the optical systemwhile the laser light is focused, to reproduce the recorded information.The reflection light reflected from the phase change recording medium isreceived by a light receiving device via the optical system, and thereceived light is subjected to a photoelectric treatment, resulting information of reproduction signals.

[0070] The optical recording medium for use in the informationrecord/reproduction apparatus of the first embodiment has a constitutionsuch that a first dielectric layer, a recording layer, a seconddielectric layer, a third dielectric layer, and areflection/heat-releasing layer (hereinafter referred to as a reflectionlayer) are formed on a substrate in this order.

[0071] Specific examples of the materials for use as the substrateinclude glass, ceramics, and resins. Among these materials, resinsubstrates are preferable in view of moldability and cost. Specificexamples of the resins for use as the substrate include polycarbonateresins, acrylic resins, epoxy resins, polystyrene resins, siliconeresins, fluorine-containing resins, ABS resins, urethane resins, etc.Among these resins, polycarbonate resins are preferable because ofhaving good processability and optical properties. The form of thesubstrate is not limited to disc forms and card-form and sheet-formsubstrates can also be used.

[0072] The first dielectric layer of the phase change optical recordingmedium is formed, for example, by sputtering (ZnS)₈₀(SiO₂)₂₀. The firstdielectric layer functions as a heat-resistant protective layer and anoptical interference layer. In order to maximally fulfill the functions,the first dielectric layer preferably has a thickness of from 20 nm to250 nm. When the first dielectric layer is too thin, the function of theheat-resistant protective layer is hardly fulfilled. In contrast, whenthe first dielectric layer is too thick, the layer tends to be peeledfrom the substrate or the adjacent layer.

[0073] The recording layer of the optical recording medium is formed,for example, by sputtering a target material which is synthesized so asto have a predetermined formula. The recording layer preferably has athickness of from 10 to 30 nm. When the recording layer is too thin, thelight absorbing ability deteriorates, and thereby the function of therecording layer is hardly fulfilled. In contrast, when the recordinglayer is too thick, the interference effect deteriorates because thequantity of the transmitted light decreases.

[0074] The second dielectric layer of the phase change optical recordingmedium is formed, for example, by sputtering (ZnS)₈₀(SiO₂)₂₀. The seconddielectric layer preferably has a thickness of from 10 nm to 40 nm. Whenthe second dielectric layer is too thin, the recording sensitivity andheat resistance deteriorates. In contrast, when the second dielectriclayer is too thick, heat is not easily radiated (i.e., heat is stored inthe recording medium).

[0075] The third dielectric layer of the phase change optical recordingmedium is formed, for example, by sputtering SiC. The third dielectriclayer preferably has a thickness of from 2 nm to 20 nm. When the thirddielectric layer is too thin, the preservation property of the recordingmedium deteriorates because Ag₂S tends to be generated when Ag is usedin the reflection layer. In contrast, when the third dielectric layer istoo thick, the recording properties deteriorate.

[0076] The reflection layer is formed, for example, by sputtering asilver alloy. The reflection layer preferably has a thickness of from 30nm to 250 nm. When the reflection layer is too thick, the recordingsensitivity deteriorates because the reflection layer has too good heatreleasing efficiency. In contrast, when the reflection layer is toothin, the overwriting properties deteriorate although the recordingsensitivity is good.

[0077] A first embodiment of the information record/reproductionapparatus utilizing the information recording method of the presentinvention will be explained.

[0078] In the first embodiment, the last heating pulse Br has a pulsewidth of from 0.5T to 0.9T and the last cooling pulse Cr has a pulsewidth of from 0.7T to 1.3T when record marks having a mark length offrom 6T to 14T are recorded. By controlling the pulse widths, theresultant record marks have a clear rear edge even when high speedrecording is performed, resulting in decrease of jitters of thereproduced signals.

[0079] Then a second embodiment of the information record/reproductionapparatus will be explained. In the second embodiment, when record markshaving a mark length of from 6T to 14T are recorded, the rear heatingpulses B have a pulse width of from 0.8T to 1.4T, and the first heatingpulse A has a pulse width of from 0.7T to 1.3T under the pulseconditions mentioned above in the first embodiment.

[0080] Since marks having a mark length of from 6T to 14T are formed byirradiating the rear heating pulses B having such a pulse width asmentioned above, the resultant record marks have a clear shape withoutnarrowing. This is because the central portion of the record markshaving such a mark length are recorded using rear heating pulses havinga wide pulse width even when high speed recording is performed.

[0081] In addition, since the first heating pulse A has such a pulsewidth as mentioned above when the marks having a mark length of from 6Tto 14T are recorded, the resultant record marks have a clear front edgeeven in high speed recording, resulting in decrease of jitters of thereproduction signals.

[0082] Then the third embodiment will be explained. In the thirdembodiment, when record marks having a mark length of 3T are recorded,the first heating pulse A has a pulse width of from 0.8T to 1.4T, andthe last cooling pulse Cr has a pulse width of from 1.1T to 1.9T underthe pulse conditions mentioned above in the first and secondembodiments.

[0083] Since the first heating pulse A has such a pulse width asmentioned above when marks having a mark length of 3T are formed, theresultant record marks have a clear front edge even in high speedrecording, resulting in decrease of jitters of the reproduction signals.

[0084] In addition, since the last cooling pulse Cr has such a pulsewidth as mentioned above when the marks having a mark length of 3T arerecorded, the resultant record marks have a clear rear edge even in highspeed recording, resulting in decrease of jitters of the reproductionsignals.

[0085] Then the fourth embodiment will be explained. In the fourthembodiment, when record marks having a mark length of 4T are recorded,the first heating pulse A has a pulse width of from 0.6T to 1.4T, thelast heating pulse Br has a pulse width of from 0.1T to 0.8T, and thelast cooling pulse Cr has a pulse width of from 0.8T to 1.7T under thepulse conditions mentioned above in the first, second and thirdembodiments.

[0086] Since the first heating pulse A has such a pulse width asmentioned above even when marks having a mark length of 4T are formed,the resultant record marks have a clear front edge even in high speedrecording, resulting in decrease of jitters of the reproduction signals.

[0087] In addition, since the last heating pulse Br has such a pulsewidth as mentioned above when the marks having a mark length of 4T arerecorded, the resultant record marks have a clear rear edge even in highspeed recording, resulting in decrease of jitters of the reproductionsignals.

[0088] In addition, since the last cooling pulse Cr has such a pulsewidth as mentioned above when the marks having a mark length of 4T arerecorded, the resultant record marks have a clear rear edge even in highspeed recording, resulting in decrease of jitters of the reproductionsignals.

[0089] Then the fifth embodiment will be explained. In the fifthembodiment, when record marks having a mark length of 5T are recorded,the first heating pulse A has a pulse width of from 0.5T to 1.6T, thelast heating pulse Br has a pulse width of from 0.6T to 1.2T, and thelast cooling pulse Cr has a pulse width of from 0.7T to 1.6T under thepulse conditions mentioned above in the first, second, third and fourthembodiments.

[0090] Since the first heating pulse A has such a pulse width asmentioned above when marks having a mark length of ST are formed, theresultant record marks have a clear front edge even in high speedrecording, resulting in decrease of jitters of the reproduction signals.

[0091] In addition, since the last heating pulse Br has such a pulsewidth as mentioned above when the marks having a mark length of 5T arerecorded, the resultant record marks have a clear rear edge even in highspeed recording, resulting in decrease of jitters of the reproductionsignals.

[0092] In addition, since the last cooling pulse Cr has such a pulsewidth as mentioned above when the marks having a mark length of 5T arerecorded, the resultant record marks have a clear rear edge even in highspeed recording, resulting in decrease of jitters of the reproductionsignals.

[0093] Then the sixth embodiment will be explained. In the sixthembodiment, the ratio (Pe/Pw) of the erasing power (Pe) to the recordingpower (Pw) is set so as to be from 0.4 to 0.7 in addition to therecording conditions mentioned above in the first to fifth embodiments.

[0094] Since recording/erasing is performed while setting the erasingpower and recording power so as to satisfy the ratio mentioned above,the resultant marks have clear edges even when recording is repeatedlyperformed, resulting in decrease of the reproduction signals.

[0095] Then the seventh embodiment will be explained. In the seventhembodiment, the recording layer of the optical recording medium has aformula of GeαGaβSbγTe100-α-β-γ wherein α is a number of from 1 to 5 inunits of atomic percent, β is a number of from 1 to 5 in units of atomicpercent, and γ is a number of from 70 to 81 in units of atomic percent,in addition to the recording conditions mentioned above in the sixthembodiment.

[0096] Since the recording layer has such a formula as mentioned above,information can be repeatedly recorded in a melt-erase mode even at ahigh recording speed of from 14 to 17.5 m/s. In this case, jitters ofthe reproduced signals can be decreased.

[0097] Then the eighth embodiment will be explained. In the eighthembodiment, the upper limit recrystallization linear speed, below whichthe recording layer heated by laser light having an erasing power of Perecrystallizes is from 14 m/s to 20 m/s.

[0098] Since the recording layer has such a property, information can bewell-recorded even at a high recording speed of from 14 to 17.5 m/s,i.e., at a speed four to five times the reproduction speed of DVD-ROMs.

[0099] The ninth embodiment will be explained. In the ninth embodiment,the recording layer of the optical recording medium has such a propertyas to crystallize at a temperature of from 160 to 210° C. when beingheated at a heating speed of 10° C./min.

[0100] Since the recording layer has such a property, information can bewell-recorded even at a high recording speed of from 14 to 17.5 m/s,i.e., at a speed four to five times that of the reproduction speed ofDVD-ROMs.

[0101] Then the tenth embodiment of the present invention will beexplained. In the tenth embodiment, the first dielectric layer has athickness of from 20 nm to 250 nm; the recording layer has a thicknessof from 10 nm to 30 nm; the second dielectric layer has a thickness offrom 10 nm to 40 nm; the third dielectric layer has a thickness of from2 nm to 20 nm; and the reflection layer has a thickness of from 30 nm to250 nm.

[0102] When each of the layers has such a thickness as mentioned above,information can be well-recorded even at a high speed.

[0103] Having generally described this invention, further understandingcan be obtained by reference to certain specific examples which areprovided herein for the purpose of illustration only and are notintended to be limiting.

EXAMPLES Example 1

[0104] In the first embodiment of the information record/reproductionapparatus, recording data are recorded in a phase change recordingmedium while applying laser light having waveform as illustrated inFIGS. 2 and 3. The resultant marks have a predetermined mark length evenwhen the record channel clock is highly frequented.

[0105] When a mark having a shortest mark length of 3T is recorded,multi-pulse laser light constituted of a first heating pulse A having apulse width of 1.0T, and a last cooling pulse Cr having a pulse width of1.4T irradiates the optical recording medium.

[0106] When a mark having a mark length of 4T is recorded, multi-pulselaser light constituted of a first heating pulse A having a pulse widthof 1.0T, a rear cooling pulse C1 having a pulse width of 1.0T, a lastheating pulse Br having a pulse width of 0.5T and a last cooling pulseCr having a pulse width of 1.3T irradiates the optical recording medium.

[0107] When a mark having a mark length of 5T is recorded, multi-pulselaser light constituted of a first heating pulse A having a pulse widthof 1.0T, a rear cooling pulse C1 having a pulse width of 1.5T, a lastheating pulse Br having a pulse width of 0.9T and a last cooling pulseCr having a pulse width of 1.1T irradiates the optical recording medium.

[0108] When a mark having a mark length of 6T is recorded, multi-pulselaser light constituted of a first heating pulse A having a pulse widthof 1.0T, rear cooling pulses C1 and C2 having a pulse width of 1.0T, arear heating pulse B1 having a pulse width of 1.0T, a last heating pulseBr having a pulse width of 0.7T and a last cooling pulse Cr having apulse width of 1.0T irradiates the optical recording medium.

[0109] When a mark having a mark length of 7T is recorded, multi-pulselaser light constituted of a first heating pulse A having a pulse widthof 1.0T, a rear cooling pulse C1 having a pulse width of 1.5T, a rearcooling pulse C2 having a pulse width of 1.3T, a rear heating pulse B1having a pulse width of 1.0T, a last heating pulse Br having a pulsewidth of 0.7T and a last cooling pulse Cr having a pulse width of 1.0Tirradiates the optical recording medium.

[0110] When a mark having a mark length of 8T is recorded, multi-pulselaser light constituted of a first heating pulse A having a pulse widthof 1.0T, rear cooling pulses C1, C2 and C3 each having a pulse width of1.0T, rear heating pulses B1 and B2 each having a pulse width of 1.0T, alast heating pulse Br having a pulse width of 0.7T and a last coolingpulse Cr having a pulse width of 1.0T irradiates the optical recordingmedium.

[0111] When a mark having a mark length of 9T is recorded, multi-pulselaser light constituted of a first heating pulse A having a pulse widthof 1.0T, a rear cooling pulse C1 having a pulse width of 1.5T, a rearcooling pulse C2 having a pulse width of 1.0T, a rear cooling pulse C3having a pulse width of 1.3T, rear heating pulses B1 and B2 each havinga pulse width of 1.0T, a last heating pulse Br having a pulse width of0.7T and a last cooling pulse Cr having a pulse width of 1.0T irradiatesthe optical recording medium.

[0112] When a mark having a mark length of 10T is recorded, multi-pulselaser light constituted of a first heating pulse A having a pulse widthof 1.0T, rear cooling pulses C1, C2, C3 and C4 each having a pulse widthof 1.0T, rear heating pulses B1, B2 and B3 each having a pulse width of1.0T, a last heating pulse Br having a pulse width of 0.7T and a lastcooling pulse Cr having a pulse width of 1.0T irradiates the opticalrecording medium.

[0113] When a mark having a mark length of 11T is recorded, multi-pulselaser light constituted of a first heating pulse A having a pulse widthof 1.0T, a rear cooling pulse C1 having a pulse width of 1.5T, rearcooling pulses C2 and C3 each having a pulse width of 1.0T, a rearcooling pulse C4 having a pulse width of 1.3T, rear heating pulses B1,B2 and B3 each having a pulse width of 1.0T, a last heating pulse Brhaving a pulse width of 0.7T and a last cooling pulse Cr having a pulsewidth of 1.0T irradiates the optical recording medium.

[0114] When a mark having a mark length of 14T is recorded, multi-pulselaser light constituted of a first heating pulse A having a pulse widthof 1.0T, rear cooling pulses C1, C2, C3, C4, C5 and C6 each having apulse width of 1.0T, rear heating pulses B1, B2, B3, B4 and B5 eachhaving a pulse width of 1.0T, a last heating pulse Br having a pulsewidth of 0.7T and a last cooling pulse Cr having a pulse width of 1.0Tirradiates the optical recording medium.

[0115] The optical recording medium used in Example 1 has a constitutionsuch that information recorded in the recording medium can also bereproduced by an information reproduction method for DVD-ROMs.

[0116] The method for preparing the optical recording medium will beexplained. A polycarbonate disc substrate having a diameter of 12 cm anda thickness of 0.6 mm was used as the substrate. In addition, a groovewas previously formed on the substrate at a pitch of 0.74 um. Thepolycarbonate substrate was subjected to a dehydration treatment at ahigh temperature. Then a first dielectric layer, a recording layer, asecond dielectric layer, a third dielectric layer and a reflection layerwere overlaid on the substrate in this order by sputtering.

[0117] When the first dielectric layer was formed, a material ZnS—SiO₂was used as a target. The thickness of the resultant first dielectriclayer was 180 nm.

[0118] The recording layer was formed while an alloy Ge₃Ga₅Sb₇₅Te₁₇(atomic %) was used as a target. Sputtering was performed underconditions of 3×10⁻³ Torr (i.e., 0.4 Pa) in the argon gas pressure and300 mW (i.e., 0.3 W) in the RF power. The thickness of the recordinglayer was 20 nm.

[0119] The second dielectric layer was formed while a material ZnS—SiO₂was used as a target. The thickness of the second dielectric layer was20 nm.

[0120] The third dielectric layer was formed while a material SiC wasused as a target. The thickness of the third dielectric layer was 6 nm.

[0121] The reflection layer was formed while a silver alloy was used asa target. The thickness of the reflection layer was 120 nm.

[0122] In addition, an organic protective layer was formed on thereflection layer by coating an ultraviolet-crosslinking acrylic resinusing a spinner so as to have a thickness of from 5 to 10 μm. Theacrylic resin was crosslinked by ultraviolet rays.

[0123] In addition, another polycarbonate disc having a diameter of 12cm and a thickness of 0.6 mm was adhered thereto using an adhesivesheet. The recording layer of the thus prepared optical recording mediumwas exposed to laser light to be initially crystallized.

[0124] In Example 1, a pickup emitting laser light having a wavelengthof 660 nm and a NA (numerical aperture of lens) of 0.65 was used forreproduce the recorded information. Recording was performed using apulse modulation method. The modulation method used is an EFM method(i.e., Eight to Sixteen Modulation). The ratio (Pe/Pw) of the erasingpower (Pe) to the recording power (Pw) was 0.5. The reproduction powerwas 0.7 mW (i.e., 0.0007W). Recording and overwriting were performed ata line density of 0.267 μm/bit. Jitter a was determined by measuring“data to clock”. Namely, jitter was determined by measuring thedeviation of the reproduction signals (i.e., data) from the standardclock cycle T (i.e., clock). The record speed and reproduction speedwere 17.5 m/s and 3.5 m/s, respectively.

[0125] As a result, a good result such that a value σ/Tw, i.e., data toclock jitter a standardized by the window width Tw, was 10% with crosstalk (i.e., signals in a track are evaluated while signals have beenrecorded in the adjacent tracks) was obtained. In addition, themodulation of the reproduction signals and the reflectance of theoptical recording medium were 65% and 18.5%. The modulation is definedas a ratio (I14/I14top) of the signal width (I14) to the signalintensity (I14top) of the top of the longest mark 14T. Further, evenafter overwriting was performed 1000 times, the standardized jitter(σ/Tw) was 11%, i.e., increase of jitter can be prevented.

[0126] In addition, when recording was performed at a speed less than17.5 m/s, good results could be obtained.

Comparative Example 1

[0127] Information was recorded at a speed of 17.5 m/s using aninformation record/reproduction apparatus which applies multi-pulselaser light as illustrated in FIG. 19 in which a pair of a heating pulseand a cooling pulse is added when the mark length increases by 1T(hereinafter referred to as a 1T strategy).

[0128] As a result, the initial jitter σ/Tw and modulation were 15% and30%, respectively. In addition, overwriting was not performed.

[0129] At the present time, the upper limit of the power at which alaser diode can stably emit light having a wavelength of 660 nm is 15 mW(i.e., 0.015W) when measured on the surface of an optical recordingmedium. When recording is performed on an optical recording medium at ahigh speed of 17.5 m/s using 660 nm laser light and 1T strategy, theoptical recording medium cannot be sufficiently heated or cooled (i.e.,the power is insufficient). Therefore, the modulation decreases and thejitter deteriorates.

[0130] In contrast, even when a laser diode of 660 nm is used, by usingthe method of Example 1 in which laser light having waveforms asillustrated in FIG. 2 irradiates, the wave length of the pulses of thelaser light corresponding to the front and rear edge portions of marksis wide, and thereby the jitter of reproduced signals can be decreasedand the modulation can be increased.

Example 2

[0131] The procedure for recording and reproduction in Example 1 wasrepeated except that the wavelength of the last heating pulse Br waschanged from 0.4T to 1.0T when marks having a mark length of from 6T to14T were recorded. The results (σ/Tw) are shown in FIG. 4. As can beunderstood from FIG. 4, when the pulse width of the last heating pulseBr is from 0.5T to 0.9T, the jitter (σ/Tw) is not greater than 14%. Tothe contrary, when the last heating pulse Br is less than 0.5T orgreater than 0.9T, the rear edges of the resultant marks become unclear,resulting in deterioration of jitter.

[0132] Accordingly, when marks having a mark length of from 6T to 14Tare recorded, the pulse width of the last heating pulse Br is set so asto be from 0.5T to 0.9T to form marks having a clear rear edge,resulting in decrease of jitter of reproduction signals.

Example 3

[0133] The procedure for recording and reproduction in Example 1 wasrepeated except that the wavelength of the last cooling pulse Cr waschanged from 0.6T to 1.4T when marks having a mark length of from 6T to14T were recorded. The results (σ/Tw) are shown in FIG. 5. As can beunderstood from FIG. 5, when the pulse width of the last cooling pulseCr is from 0.7T to 1.3T, the jitter (σ/Tw) is not greater than 14%. Tothe contrary, when the last cooling pulse Cr is less than 0.7T orgreater than 1.3T, the rear edges of the resultant marks become unclear,resulting in deterioration of jitter.

[0134] Accordingly, when marks having a mark length of from 6T to 14Tare recorded, the pulse width of the last cooling pulse Cr is set so asto be from 0.7T to 1.3T to form marks having a clear rear edge,resulting in decrease of jitter of reproduction signals.

Example 4

[0135] The procedure for recording and reproduction in Example 1 wasrepeated except that the wavelength of the rear heating pulses B1 to B5were changed from 0.7T to 1.5T when marks having a mark length of from6T to 14T were recorded. The results (σ/Tw) are shown in FIG. 6. As canbe understood from FIG. 6, when the pulse width of the rear heatingpulses B1 to B5 are from 0.8T to 1.4T, the jitter (σ/Tw) is not greaterthan 14%. To the contrary, when the pulse width of the rear heatingpulses B1 to B5 is less than 0.8T, the resultant marks narrow due toinsufficient power, resulting in deterioration of jitter.

[0136] In contrast, when the pulse width of the rear heating pulse B1 toB5 is greater than 1.4T, the resultant marks narrow due to insufficientcooling time, resulting in deterioration of jitter.

[0137] Accordingly, when marks having a mark length of from 6T to 14Tare recorded, the pulse width of the rear heating pulses B1 to B5 is setso as to be from 0.8T to 1.4T to prevent narrowing of recorded marks,resulting in decrease of jitter of reproduction signals.

Example 5

[0138] The procedure for recording and reproduction in Example 1 wasrepeated except that the wavelength of the first heating pulse A waschanged from 0.6T to 1.4T when marks having a mark length of from 6T to14T were recorded. The results (σ/Tw) are shown in FIG. 7. As can beunderstood from FIG. 7, when the pulse width of the first heating pulseA is from 0.7T to 1.3T, the jitter (σ/Tw) is not greater than 14%. Tothe contrary, when the pulse width of the first heating pulse A is lessthan 0.7T, the front edge of the resultant marks narrows due toinsufficient power, resulting in deterioration of jitter. When the pulsewidth of the first heating pulse A is greater than 1.3T, the front edgeof the resultant marks narrows due to insufficient cooling time,resulting in deterioration of jitter.

[0139] Accordingly, when marks having a mark length of from 6T to 14Tare recorded, the pulse width of the first heating pulse A is set so asto be from 0.7T to 1.3T to prevent narrowing of the front edges of themarks, resulting in decrease of jitter of reproduction signals.

Example 6

[0140] The procedure for recording and reproduction in Example 1 wasrepeated except that the wavelength of the first heating pulse A waschanged from 0.7T to 1.5T when marks having a mark length of 3T wererecorded. The results (σ/Tw) are shown in FIG. 8. As can be understoodfrom FIG. 8, when the pulse width of the first heating pulse A is from0.8T to 1.4T, the jitter (σ/Tw) is not greater than 14%. To thecontrary, when the pulse width of the first heating pulse A is less than0.8T, the front edge of the resultant marks narrows due to insufficientpower, resulting in deterioration of jitter. When the pulse width of thefirst heating pulse A is greater than 1.5T, the front edge of theresultant marks narrows due to insufficient cooling time, resulting indeterioration of jitter.

[0141] Accordingly, when marks having a mark length of 3T are recorded,the pulse width of the first heating pulse A is set so as to be from0.8T to 1.4T to prevent narrowing of the front edges of the marks,resulting in decrease of jitter of reproduction signals.

Example 7

[0142] The procedure for recording and reproduction in Example 1 wasrepeated except that the wavelength of the last cooling pulse Cr waschanged from 1.0T to 2.0T when marks having a mark length of 3T wererecorded. The results (σ/Tw) are shown in FIG. 9. As can be understoodfrom FIG. 9, when the pulse width of the last cooling pulse Cr is from1.1T to 1.9T, the jitter (σ/Tw) is not greater than 14%. To thecontrary, when the pulse width of the last cooling pulse Cr is less than1.1T or greater than 1.9T, the resultant marks have an unclear rearedge, resulting in deterioration of jitter.

[0143] Accordingly, when marks having a mark length of 3T are recorded,the pulse width of the last cooling pulse Cr is set so as to be from1.1T to 1.9T to form marks having a clear rear edge, resulting indecrease of jitter of reproduction signals.

Example 8

[0144] The procedure for recording and reproduction in Example 1 wasrepeated except that the wavelength of the first heating pulse A waschanged from 0.5T to 1.5T when marks having a mark length of 4T wererecorded. The results (σ/Tw) are shown in FIG. 10. As can be understoodfrom FIG. 10, when the pulse width of the first heating pulse A is from0.6T to 1.4T, the jitter (σ/Tw) is not greater than 14%. To thecontrary, when the pulse width of the first heating pulse A is less than0.6T, the front edge of the resultant marks narrows due to insufficientpower, resulting in deterioration of jitter. When the pulse width of thefirst heating pulse A is greater than 1.4T, the front edge of theresultant marks narrows due to insufficient cooling time, resulting indeterioration of jitter.

[0145] Accordingly, when marks having a mark length of 4T are recorded,the pulse width of the first heating pulse A is set so as to be from0.6T to 1.4T to prevent narrowing of the front edges of the marks,resulting in decrease of jitter of reproduction signals.

Example 9

[0146] The procedure for recording and reproduction in Example 1 wasrepeated except that the wavelength of the last heating pulse Br waschanged from 0.1T to 0.9T when marks having a mark length of 4T wererecorded. The results (σ/Tw) are shown in FIG. 1. As can be understoodfrom FIG. 11, when the pulse width of the last heating pulse Br is from0.1T to 0.8T, the jitter (σ/Tw) is not greater than 14%. To thecontrary, when the pulse width of the last heating pulse Br is less than0.1T or greater than 0.9T, the resultant marks have an unclear rearedge, resulting in deterioration of jitter.

[0147] Accordingly, when marks having a mark length of 4T are recorded,the pulse width of the last heating pulse Br is set so as to be from0.1T to 0.8T to form marks having a clear rear edge, resulting indecrease of jitter of reproduction signals.

Example 10

[0148] The procedure for recording and reproduction in Example 1 wasrepeated except that the wavelength of the last cooling pulse Cr waschanged from 0.7T to 1.8T when marks having a mark length of 4T wererecorded. The results (σ/Tw) are shown in FIG. 12. As can be understoodfrom FIG. 12, when the pulse width of the last cooling pulse Cr is from0.8T to 1.7T, the jitter (σ/Tw) is not greater than 14%. To thecontrary, when the pulse width of the last cooling pulse Cr is less than0.8T or greater than 1.7T, the resultant marks have an unclear rearedge, resulting in deterioration of jitter.

[0149] Accordingly, when marks having a mark length of 4T are recorded,the pulse width of the last cooling pulse Cr is set so as to be from0.8T to 1.7T to form marks having a clear rear edge, resulting indecrease of jitter of reproduction signals.

Example 11

[0150] The procedure for recording and reproduction in Example 1 wasrepeated except that the wavelength of the first heating pulse A waschanged from 0.4T to 1.7T when marks having a mark length of 5T wererecorded. The results (σ/Tw) are shown in FIG. 13. As can be understoodfrom FIG. 13, when the pulse width of the first heating pulse A is from0.5T to 1.6T, the jitter (σ/Tw) is not greater than 14%. To thecontrary, when the pulse width of the first heating pulse A is less than0.5T, the front edge of the resultant marks narrows due to insufficientpower, resulting in deterioration of jitter. When the pulse width of thefirst heating pulse A is greater than 1.6T, the front edge of theresultant marks narrows due to insufficient cooling time, resulting indeterioration of jitter.

[0151] Accordingly, when marks having a mark length of 5T are recorded,the pulse width of the first heating pulse A is set so as to be from0.5T to 1.6T to prevent narrowing of the front edges of the marks,resulting in decrease of jitter of reproduction signals.

Example 12

[0152] The procedure for recording and reproduction in Example 1 wasrepeated except that the wavelength of the last heating pulse Br waschanged from 0.5T to 1.3T when marks having a mark length of 5T wererecorded. The results (σ/Tw) are shown in FIG. 14. As can be understoodfrom FIG. 14, when the pulse width of the last heating pulse Br is from0.6T to 1.2T, the jitter (σ/Tw) is not greater than 14%. To thecontrary, when the pulse width of the last heating pulse Br is less than0.6T or greater than 1.2T, the resultant marks have an unclear rearedge, resulting in deterioration of jitter.

[0153] Accordingly, when marks having a mark length of 5T are recorded,the pulse width of the last heating pulse Br is set so as to be from0.6T to 1.2T to form marks having a clear rear edge, resulting indecrease of jitter of reproduction signals.

Example 13

[0154] The procedure for recording and reproduction in Example 1 wasrepeated except that the wavelength of the last cooling pulse Cr waschanged from 0.6T to 1.7T when marks having a mark length of 5T wererecorded. The results (σ/Tw) are shown in FIG. 15. As can be understoodfrom FIG. 15, when the pulse width of the last cooling pulse Cr is from0.7T to 1.6T, the jitter (σ/Tw) is not greater than 14%. To thecontrary, when the pulse width of the last cooling pulse Cr is less than0.7T or greater than 1.6T, the resultant marks have an unclear rearedge, resulting in deterioration of jitter.

[0155] Accordingly, when marks having a mark length of 5T are recorded,the pulse width of the last cooling pulse Cr is set so as to be from0.7T to 1.6T to form marks having a clear rear edge, resulting indecrease of jitter of reproduction signals.

Example 14

[0156] The procedure for recording and reproduction in Example 1 wasrepeated except that the ratio (Pe/Pw) of the erasing power (Pe) to therecording power (Pw) was changed so as to be 0.3, 0.4, 0.5, 0.6 and 0.7.The jitter after repeated recording is shown in FIG. 16. As can beunderstood from FIG. 16, when the ratio (Pe/Pw) is 0.4 to 0.7, thejitter (σ/Tw) is not greater than 10% even after recording is repeated1000 times. When the ratio (Pe/Pw) is 0.3, the jitter, particularly theinitial jitter, is inferior to the jitter when the ratio is 0.4 to 0.7.In particular, when recording is repeated twice, the jitter seriouslyincreases. In contrast, when the ratio (Pe/Pw) is not less than 0.8, therecording layer achieves an amorphous state because the erase power istoo large.

[0157] The reason is considered to be that when the ratio is from 0.4 or0.7, the recording layer is melted and then recrystallized (i.e.,recording is performed in a melt-erase mode), but when the ratio is 0.3,the recording layer is not melted due to low erasing power and therebythe recording layer recrystallizes while maintaining a solid state.Namely, the recrystallization mode is different in both the cases, andthereby the jitter are different.

[0158] Accordingly, by setting the ratio (Pe/Pw) so as to be 0.4 to 0.7,marks having a clear edge can be formed even in high speed recording,resulting in decrease of jitter even after repeated use.

Examples 15 to 22 and Comparative Examples 2 to 5

[0159] The procedure for preparation of the optical recording medium inExample 1 was repeated except that the formula of the recording layerwas changed as shown in Table 1. Information was repeatedly recorded inthe resultant recording media under the following conditions:

[0160] Recording linear speed: 17.5 m/s

[0161] Recording power Pw: 15 mW (i.e., 0.015W)

[0162] Erasing power Pe: 8 mW (i.e., 0.008W)

[0163] The information-recorded optical recording media were evaluatedas follows:

[0164] Each information-recorded optical recording medium was allowed tosettle in an oven for 300 hours under the conditions 80° C. intemperature and 85% in relative humidity to determine jitters before andafter the preservation test (i.e., jitter increasing rate; so-calledarchival increasing rate). In addition, the crystallization temperatureand melting point of the film of each recording layer were measured at atemperature rising speed of 10° C./min.

[0165] Further, the repeatability (i.e., as to how many timesinformation can be recorded therein with a jitter not greater than 14%)was evaluated. The results are shown in Table 2. TABLE 1 Formula of therecording layer (atomic %) Sb Te Ge Ga Example 15 76 18.1 3 2.9 Example16 77 15.6 2.9 4.5 Example 17 72 18 5 5 Example 18 76 16 5 3 Example 1979 14 4.5 2.5 Example 20 73 21 3 3 Example 21 77 15 4 4 Example 22 72 231 4 Comparative 85 5 5 5 Example 2 Comparative 67 20 4 9 Example 3Comparative 68 17 10 5 Example 4 Comparative 76 21 0 3 Example 5

[0166] TABLE 2 Repeat- Crystal- Jitter Initial Melting Ability lizationincreas- crystal- point (times) temp. (° C.) ing rate lization (° C.)Ex. 15 12000 175 1.2 Good 545 Ex. 16 10000 185 1.2 Good 530 Ex. 17 11000190 1.3 Good 550 Ex. 18 12000 175 1.2 Good 535 Ex. 19 12000 170 1.1 Good540 Ex. 20 11000 175 1.2 Good 550 Ex. 21 10000 180 1.3 Good 540 Ex. 228000 180 1.2 Good 535 Comp. 300 170 8 Good 530 Ex. 2 Comp. 500 230 4Impos- 530 Ex. 3 sible Comp. 1 180 3 Good 530 Ex. 4 Comp. 500 170 7 Good530 Ex. 5

[0167] In Examples 15 to 22 and Comparative Examples 2 to 5, the formulaof the recording layer of the optical recording medium of Example 1 ischanged such that the recording layer has a crystallization temperatureof from 170 to 230° C. when measured at a temperature rising speed of10° C./min.

[0168] As can be understood from Tables 1 and 2, the optical recordingmedia have a good repeatability not less than 5000 times, and a goodjitter property (a low jitter increasing rate not greater than 1.3%;i.e., jitter hardly increases even after the preservation test). Inaddition, the re-crystallization speed of the recording layers is notless than 14 m/s.

[0169] Further, information could be well-recorded in the opticalrecording media of Examples 15 to 22 even at a low speed less than 17.5m/s.

[0170] In contrast, since Sb is included in the recording layer of theoptical recording medium of Comparative Example 2 at a high content of85 atomic %, the optical recording medium has a poor preservationproperty, and a poor repeatability.

[0171] Since Ga is included in the recording layer of the opticalrecording medium of Comparative Example 3 at a high content of 9 atomic%, the recording layer of the optical recording medium has a highcrystallization temperature of 230° C., and thereby initialcrystallization cannot be performed on the recording layer.

[0172] Since Ge is included in the recording layer of the opticalrecording medium of Comparative Example 4 at a high content of 10 atomic%, the crystallization speed is slow, specifically the recording layerhas a low re-crystallization speed of 12 m/s. Therefore, when erasure isperformed at a speed of 17.5 m/s, an amorphous region remains in therecording layer, resulting in deterioration of the repeated recordingproperty.

[0173] Since Ge is not included in the recording layer of the opticalrecording medium of Comparative Example 5, the recording medium has poorpreservability.

[0174] Thus, since the optical recording media of Examples 15 to 22 havea crystallization temperature of from 160° C. to 210° C. when measuredat a temperature rising speed of 10° C./min, initialization can beeasily performed and in addition the resultant optical recording mediahave a good preservation property.

[0175] Effects of the Present Invention

[0176] According to the information recording method of the presentinvention, by controlling each of the pulse width of the last heatingpulse and last cooling pulse so as to fall in a specific range, markshaving clear rear edges can be recorded even at a high recording speed,thereby preventing increase of jitter of reproduction signals.

[0177] In addition, by controlling each of the pulse widths of the rearheating pulses and first heating pulse so as to fall in a specific rangewhen marks having a mark length of from 6T to 14T, a problem in that thecentral portion of the record marks having a mark length of from 6T to14T narrows can be prevented, and in addition the front edge of themarks is clear even at a high recording speed, thereby preventingincrease of jitter of reproduction signals.

[0178] By further controlling each of the pulse widths of the firstheating pulse and last cooling pulse so as to fall in a specific rangewhen marks having a mark length of 3T are recorded, the resultant markswith a mark length of 3T have a clear front edge and a clear rear edgeeven at a high recording speed, thereby preventing increase of jitter ofreproduction signals.

[0179] By further controlling each of the pulse widths of the firstheating pulse, last heating pulse and last cooling pulse so as to fallin a specific range when marks having a mark length of 4T are recorded,the resultant marks with a mark length of 4T have a clear front edge anda clear rear edge even at a high recording speed, thereby preventingincrease of jitter of reproduction signals.

[0180] In addition, by further controlling each of the pulse widths ofthe first heating pulse, last heating pulse and last cooling pulse so asto fall in a specific range when marks having a mark length of 5T arerecorded, the resultant marks with a mark length of 5T have a clearfront edge and a clear rear edge even at a high recording speed, therebypreventing increase of jitter of reproduction signals.

[0181] Further, when the ratio (Pe/Pw) of the erasing power (Pe) to therecording power (Pw) is from 0.4 to 0.7, the resultant marks have clearedges, thereby preventing increase of jitter of production signals evenafter repeated use.

[0182] When the recording layer of the optical recording medium used hasa specific formula, information can be repeatedly recorded in amelt-erase mode even at a high recording speed, thereby preventingincrease of jitter of reproduction signals.

[0183] In addition, when the upper-limit of re-crystallization linearspeed of the recording layer is in a specific range, information can bewell-recorded therein even at a high recording speed of from 14 to 17.5m/s, i.e., a speed 4 to 5 times the reproduction speed for DVD-ROMs.

[0184] When the recording layer has a specific crystallizationtemperature, the recording medium can be easily initialized and has goodpreservation stability.

[0185] Additional modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced other than as specifically described herein.

[0186] This document claims priority and contains subject matter relatedto Japanese Patent Application No. 2002-021361, filed on Jan. 30, 2002,the entire contents of which are herein incorporated by reference.

What is claimed is:
 1. An information recording method comprising:irradiating a phase-change recording layer of an optical recordingmedium with either a multi-pulse laser light train having a recordingpower of Pw or laser light having an erasing power Pe to allow thephase-change recording layer to reversibly achieve a crystal state andan amorphous state, thereby recording a mark having a mark length nT inthe recording layer, wherein n is an integer of from 3 to 14 and Trepresents a clock cycle, wherein the multi-pulse laser light train hasa constitution such that a heating pulse and a cooling pulse arealternated, wherein the number of heating pulses and the number ofcooling pulses each increases by one when n increases by two, andwherein when n is from 6 to 14, a last heating pulse has a pulse widthof from 0.5T to 0.9T and a last cooling pulse has a pulse width of from0.7T to 1.5T.
 2. The information recording method according to claim 1,wherein when n is from 6 to 14, a first heating pulse has a pulse widthof from 0.7T to 1.3T and a rear heating pulse, which is located betweenthe first heating pulse and the last heating pulse, has a pulse width offrom 0.8T to 1.4T.
 3. The information recording method according toclaim 1, wherein when n is 3, the first heating pulse has a width offrom 0.8T to 1.4T and the last cooling pulse has a width of from 1.1T to1.9T.
 4. The information recording method according to claim 1, whereinwhen n is 4, the first heating pulse has a width of from 0.6T to 1.4T,the last heating pulse has a width of from 0.1T to 0.8T and the lastcooling pulse has a width of from 0.8T to 1.7T.
 5. The informationrecording method according to claim 1, wherein when n is 5, the firstheating pulse has a width of from 0.5T to 1.6T, the last heating pulsehas a width of from 0.6T to 1.2T and the last cooling pulse has a widthof from 0.7T to 1.6T.
 6. The information recording method according toclaim 1, wherein a ratio (Pe/Pw) of the erasing power (Pe) to therecording power (Pw) is from 0.4 to 0.7.
 7. The information recordingmethod according to claim 1, wherein the recording layer has a formulaof GeαGaβSbγTe100-α,β-γ, wherein α is a number of from 1 to 5 in unitsof atomic percent, β is a number of from 1 to 5 in units of atomicpercent, and γ is a number of from 70 to 81 in units of atomic percent.8. The information recording method according to claim 7, wherein anupper limit recrystallization linear speed, below which the recordinglayer heated by the laser light having the erasing power Pere-crystallizes, is from 14 m/s to 20 m/s.
 9. The information recordingmethod according to claim 7, wherein the recording layer has such aproperty as to crystallize at a temperature of from 160 to 210° C. whenheated at a heating speed of 10° C./min.
 10. An optical recording mediumcomprising: a substrate; a recording layer located overlying thesubstrate, wherein the recording layer has a formula ofGeαGaβSbγTe100-α-β-γ, wherein α is a number of from 1 to 5 in units ofatomic percent, β is a number of from 1 to 5 in units of atomic percent,and γ is a number of from 70 to 81 in units of atomic percent; and areflection layer located overlying the recording layer.
 11. The opticalrecording medium according to claim 10, wherein the recording layer hasan upper limit re-crystallization linear speed of from 14 m/s to 20 m/s.12. The optical recording medium according to claim 10, wherein therecording layer has a crystallization temperature of from 160 to 210° C.when being heated at a heating speed of 10° C./min.